Compressors or fluid-compressing devices are used in various industrial sectors for various applications in which compression of fluids, in particular (process) gases, is involved. Known examples of this are turbocompressors in mobile industrial applications, such as in exhaust gas turbochargers or in jet engines, or else in stationary industrial applications, such as transmissions or transmission turbocompressors for air separation.
In such a turbocompressor, which operates continuously in its working mode, the pressure rise (compression) of the fluid is brought about in that an angular momentum of the fluid from inlet to outlet is increased by a rotating impellor, having radially extending blades, of the turbocompressor as a result of the rotation of the blades. Here, that is to say in such a compressor stage, the pressure and temperature of the fluid rise, while the relative (flow) velocity of the fluid in the impellor or turboimpellor falls.
In order to achieve as high a pressure rise or compression of the fluid as possible, a plurality of such compressor stages may be connected in series.
In terms of the forms of construction of turbocompressors, a distinction is made between radial and axial compressors.
In the axial compressor, the fluid to be compressed, for example a process gas, flows through the compressor in a direction parallel to the axis (axial direction).
In the radial compressor, the gas flows axially into the impellor of the compressor stage and is then deflected outward (radially, radial direction). In multistage radial compressors, therefore, flow deflection becomes necessary after each stage.
Combined constructions of axial and radial compressors suck in with their axial stages large volume flows which are compressed to high pressures in the following radial stages.
While single-shaft machines are mostly used, in (multistage) transmission turbocompressors (also referred to briefly below as simply transmission compressors) the individual compressor stages are grouped around a large wheel, a plurality of parallel (pinion) shafts, which each carry one or two impellors (turboimpellors arranged at free shaft ends of the pinion shafts) accommodated in spiral housings implemented as housing attachments, being driven by a large driving gearwheel, a large wheel, mounted in the housing.
Such a transmission compressor is known as a transmission compressor from Siemens with the designation STC-GC, used for air separation, and is likewise known from EP 1 067 291 A1.
In a transmission compressor, the drive and therefore the transfer of power from the large wheel to the shafts or pinion shafts take place by means of interengaging or intermeshing toothings on the large wheel and pinion shaft. Desired step-ups or step-up ratios (power stages) in the individual transmission stages are implemented via different numbers of teeth of the toothings or different reference diameters. That is to say, the individual pinion shafts are coupled to the large wheel and to one another in terms of toothing geometry and pinion shaft center position (mid-point or axis of rotation of a pinion shaft).
If a plurality of pinion shafts are arranged around the large wheel, a compromise must be found between ideal and implementable step-up ratios. A critically determining and limiting variable is in this case the available and/or implementable construction space, in particular the space available for the flow-routing components (spiral housings) arranged as housing attachments outside the housing at the pinion shaft ends.
The coupling of the pinion shafts to the large wheel via toothing geometry and the pinion shaft center position therefore assumes central importance in the development and design and also construction of transmission turbomachines. On account of the size ratios or size differences, that is to say because the large wheel is very much larger than the many times smaller pinion shafts to be arranged around the large wheel, there is, in particular, the question of the situation of the pinion shafts or their pinion shaft center positions.
In a conventional arrangement, two pinion shafts lie in a first undivided and horizontal parting joint with the large wheel. A third pinion shaft is arranged above the large wheel in a second undivided and horizontal parting joint.
In this arrangement, on the overall three pinion shafts, there are six free shaft ends which, equipped with turboimpellors, make it possible to implement a multistage transmission turbomachine with six possible process stages.
In order to increase the compression performance of such a six-stage transmission compressor, it is known to increase the number of process stages, for example by means of a fourth pinion shaft.
What is required in this case is to accommodate this fourth pinion shaft in the housing of a transmission compressor efficiently and in a straightforward way in terms of construction and assembly.
Two approaches for arranging such a fourth pinion shaft are known:
a) Arrangement of the fourth pinion shaft above the large wheel together with the third pinion shaft in the second undivided and horizontal parting joint.
If the fourth pinion shaft is arranged above the large wheel, the available construction space has to be shared with the third pinion shaft. In arranging the third and the fourth pinion shaft in the parting joint, collisions of flow-routing components (spiral housings) arranged on the outside are critical. So that interfaces with adjacent functions (bearing accommodation, spiral tie-up) can be defined, the parting joint is designed to be undivided and horizontal.
In order to implement various step-ups in the transmission stages in such an arrangement, it is known to use a multiply toothed large wheel, for example as an integrated unit with a second large wheel. That is to say, such a multiply toothed large wheel has (axially) offset toothings which mesh in each case with different pinion shafts.
Although a multiplicity of additional step-up ratios and pinion shaft center positions coupled to them are possible as a result, this nevertheless entails a high outlay in terms of manufacture and cost.
b) Arrangement of the fourth pinion shaft below the large wheel in a version as a plug-in pinion shaft.
If the fourth pinion shaft is arranged below the large wheel, the construction space does not have to be shared with an adjacent pinion shaft, but there is no parting joint there which can be used for mounting purposes.
It is possible to mount the fourth pinion shaft only by pushing (plugging) it in laterally (plug-in pinion shaft).
As a result, the pinion shaft center positions can be selected virtually freely, taking into account the spiral housings of the first parting joint. However, here too, implementation entails considerable extra outlay (mounting parts, mounting operation).